1. Field of the Invention
The present invention relates to an improved injection dart. More specifically, it relates to an improved injection dart which employs a flow restrictor which limits and controls the rate of flow of an injection administered by the dart.
2. Description of the Prior Art
Dart-type projectiles carrying a self-contained actuating means which detonate upon rapid deceleration are generally well known in delivering drugs, medicines and the like to animals from a distance. Studies have concluded the rate of injection can and will disturb living tissue and in some instances result in partial injection due to the dart being propelled away from its intended target as a result of the speed of impact coupled with the rate of the injection rate. The use of hypodermic darts to administer anesthesia or other medications to animals is well known in the art. An early example is described and shown in Harris, U.S. Pat. No. 1,815,300. A number of injecting projectiles have been proposed by Crockford et al. including U.S. Pat. Nos. 2,854,925; 2,923,243; 3,022,785; and 3,209,695. Still other dart-like projectiles are described in Murdock, U.S. Pat. No. 3,207,157 and in Warren et al., U.S. Pat. No. 3,266,806. At the present time, injection darts are typically shot as projectiles from dart-projectors into the animal.
Publication No. WO 1988010129 A1, by Allan Kenneth Wallace teaches that a large number of drug reactions are due to the rate of injection, not the species of drug and that “[i]deally, the contents of a syringe need to be delivered over a number of minutes.”
Fischer, U.S. Pat. No. 5,944,698, discloses an adjustable flow syringe. In one embodiment of the invention described in column 8, lines 24-36, Fischer teaches the provision of an adjustable flow syringe 90 which includes a porous inset 94 which is capable of performing the function of a flow restrictor means for restricting the flow rate of a fluid in the syringe such that any force within a range of forces that can be manually applied to plunger 14 delivers fluid at a substantially constant flow rate
Rosenblum, U.S. Pat. No. 2,444,677, teaches a flow control device wherein fluid flowing through the casing must flow through the fixed orifice direct to the hollow shank or through the compensating orifice and ports into the hollow shank before it is discharged from the casing. The rubber ring deflects downstream in accordance with the pressure of the fluid to vary the capacity of the compensating orifice.
Kempton, U.S. Pat. No. 2,454,929, teaches a flow control which, as shown in FIG. 5, has a resilient annular member 11 which is deformed in the region of the orifice 17 when fluid under pressure is introduced in the bore 25 and is delivered through the bore 31 in the lower coupling member 26. The extent of deformation of the resilient annular member 11 depends upon the pressure drop across the orifice, the greater the pressure drop the greater the deformation. Such deformation causes a reduction in the diameter of the orifice.
Dahl et al., U.S. Pat. No. 2,936,788, teach a flow control system wherein disposed within the hollow interior of the housing 10 is a resilient, annular flow control washer 13 composed of rubber, chlorinated rubber, or similar elastic material. The flow control washer 13 is said to be effective to maintain a substantially constant flow over a wide range of pressure variations by its automatic reduction in the cross-sectional area of its orifice 13a upon increases in pressure thereon. Dahl et al. teach the provision of a flow control washer 13 which includes a frusto-conical face 13b. 
Diggs, U.S. Pat. No. 3,833,019, teaches an irrigation system which employs a flow control device. A resilient compressible orifice member 34 is provided which has a conically shaped orifice 37 in its center. When the fitting is compressed, the compressible member to be deformed radially inwardly to decrease the size of the orifice 37 and thus restrict the rate of flow.
Taguri et al., U.S. Pat. No. 5,209,265, is yet another example of a flow control with a restrictor which includes an elastic valve 30 molded from a rubber or the like elastic material to have a small diameter section 31 and a large diameter section 32 with tapered periphery, as shown in FIG. 3. An aperture 33 is formed to extend through an axial center of the valve 30 for fluid communication between pipe 15 and passage 24. The valve 30 is capable of elastically deforming so as to vary the diameter of the aperture 33 in proportion to the pressure applied thereto, thereby allowing the water to flow through the aperture 33 at a controlled rate of keeping the flow volume at a constant level irrespective of the variation of pressure of the water being supplied.
Despite the many known examples of projectile darts and the many known methods of providing flow control, there remains a need for an improved injection dart which can address the difficult and complex problem of reliably and consistently injecting an animal with various medications at a rate which does not cause damage or injury to the tissue of the animal and does not cause the dart to eject from the animal's skin because of excessive backward pressure from a too rapid injection.